1. Field of the Invention
The present invention relates to a source coupled differential complementary Colpitts oscillator which enables a differential oscillation and also can improve phase noise performance by source-coupling a complementary Colpitts oscillator using an inductor.
2. Description of the Related Art
Generally, a complementary Colpitts oscillator using an N-channel metal-oxide semiconductor (NMOS) and P-channel metal-oxide semiconductor (PMOS) enables a self-biasing. Accordingly, the complementary Colpitts oscillator has a simple circuit structure, and the noise performance of the complementary Colpitts oscillator is superior to the negative-Gm differential oscillator.
However, the complementary Colpitts oscillator performs only a single-ended oscillation. Accordingly, the complementary Colpitts oscillator may not be applied to an integrated circuit which requires a differential oscillation. A Colpitts oscillator for a differential oscillation has been developed which induces differential oscillation by combining a plurality of complementary Colpitts oscillators. In this instance, the oscillations are output from a plurality of complementary Colpitts oscillators.
FIG. 1 is a diagram illustrating a circuit of a Colpitts oscillator for a differential oscillation according to a related art.
As illustrated in FIG. 1, the related art Colpitts oscillator for differential oscillation combines two complementary Colpitts oscillators using an NMOS and a PMOS semiconductors with a cross coupled transistor pair, thereby enabling the differential oscillation.
Specifically, the Colpitts oscillator for the differential oscillation of FIG. 1 cross combines an N-metal-oxide semiconductor field-effect transistor (N-MOSFET) and a P-metal-oxide semiconductor field-effect transistor (P-MOSFET) with an inverse complementary Colpitts oscillator, thereby inducing the differential oscillation. In this instance, the N-MOSFET and the P-MOSFET constitute a complementary Colpitts oscillator.
However, in the case of the related art Colpitts oscillator for differential oscillation, a number of inductors Ltank is increased to match the number of combined complementary Colpitts oscillators. Accordingly, a layout of the integrated circuit is expanded.
Also, in the case of the related art Colpitts oscillator for differential oscillation, a MOSFET operates in a linear mode in a comparatively greater oscillation swing. Accordingly, the quadrature (Q)-factor of a link control (LC) Tank circuit is reduced, and the phase noise performance deteriorates.
Therefore, a differential complementary Colpitts oscillator which enables a differential oscillation with low noise is highly needed.